I just got off the phone with Apple Support. The guy (who was surprisingly knowledgeable) told me that push services are not yet turned on for the desktop applications. Until they are, the desktop apps will sync about every 10 minutes (if set to automatic in preferences). However, iPhone and MobileMe push should be working.
Once desktop app push is turned on, it really only applies to Calendar and Address Book. Mail will remain IMAP, and not entirely push. If it is set to check every minute, it will be close, but not perfect. However, MobileMe and the iPhone mail app are true push. The guy had no idea why Apple decided to do that, but doesn't see it changing.